EarthquakesEarthquakes

Earthquakes Result from StressWhat is an Earthquake?–Definition :

Shaking of a crust by a release of energy– Results :

1. Explosions, fires, broken sewage lines and water mains. Unstable roads, railroads, runways.

2. Tsunamis

Tsunami:Tsunami: Giant ocean wave generated by an earthquake whose epicenter is on the ocean floor.

(computer generated photo)

Causes of EarthquakesElastic – rebound theory –Definition :

When stress overcomes friction, sudden movement occurs and a snap forward occurs.

This is followed by a rebound or snap back.

TerminologyFocus :– Where earthquakes

actually occur below the surface

Epicenter : – Point on earth’s surface directly above focus

Magnitude vs. IntensityMagnitude–Definition:

The amount of energy released by an earthquake.

Intensity–Definition:

The amount of damage caused by an earthquake.

• Intensity: Mercalli Scale Magnitude: Richter Scale

-Scale 1- 12 -Scale 1- 10 1= no damage 30 times more energy as you 12= total destruction go up the scale

Earthquake WavesKinds of wave motions– P Waves

Primary (compressional) wavesCan travel through any materials (solid, liquid, gas)Back and forth wavesTwice as fast as S waves

– S WavesSecondary waves Side to side wavesCan travel through solids only

– L WavesSurface wavesSlowest moving wavesCause the most damage

Seismograph: Instrument used to detect and record vibrations from earthquakes.Seismograph: Instrument used to detect and record vibrations from earthquakes.

Seismogram: Record of an event from seismograph

Lag Time: Since P waves travel faster than S waves, scientists determine distance to the epicenter by analyzing the difference in arrival times.

Lag Time:The longer the lag time between the

arrival of the P-waves and the arrival of the S-waves, the farther away the earthquake occurred.

Locating the epicenterLocating the epicenter

Triangulate between3 or more seismograph stations

Where the circles Intersect = an

epicenter